This invention relates to a method and apparatus for rolling hot continuously cast copper and aluminum bar. More particularly, the invention relates to a method of heat treating alloy steel work rolls of a plural stage rolling mill to prolong the useful life of the rolls and to improve the uniformity of useful life among the various roll stages. The invention also relates to improved work rolls and to a rolling mill which utilizes improved work rolls produced according to the heat treatment method of the invention.
In a conventional rolling mill, such as, for example, a Morgan Mill manufactured by Morgan Construction Co. of Worcester, Massachusetts, a continuously cast bar of non-ferrous metal is subjected to several stages of reduction, each reduction stage comprising a plurality of roll sets or stands. The roll stands are generally characterized according to their function in the rolling mill, for example, the roll stands arranged for receiving the hot continuously cast bar and for the initial reduction and working of the bar are identified as breakdown stands. Following the breakdown roll stands are intermediate roll stands sufficient in number to achieve the desired gradual reduction of the cast bar cross-section and, finally, the finishing roll stands which, in addition to some further reduction of the cast bar cross-section, are intended to provide the surfaces of the cast bar with a smooth surface for subsequent working operations, such as extrusion or drawing through dies to make wire.
In rolling mills of the aforementioned type for rolling continuously cast hot non-ferrous metals, it is known to use alloy steel work rolls to shape the metal bar. The alloy steel material from which the work rolls are fabricated must be capable of resisting the high temperatures and pressures associated with the rolling of such bars. A search of the prior art revealed that tool steels from which are fabricated work rolls used for hot-working ferrous metals usually have a substantially chromium content (13.0 to 20.0 percent by weight) and generally are characterized by high hardness and good wear resistance. The patents uncovered during the aforementioned search are listed below:
U.s. pat. No. 2,197,098; PA1 U.s. pat. No. 2,442,223; PA1 U.s. pat. No. 3,576,782; PA1 U.s. pat. No. 3,097,091; PA1 U.s. pat. No. 3,421,307; PA1 U.s. pat. No. 3,496,031; PA1 U.s. pat. No. 3,885,995.